Ultraviolet (UV) photodetectors and light emitters find numerous uses including applications in the defense, commercial, and scientific arenas. These include, for example, covert space-to-space communications, missile threat detection, chemical and biological threat detection and spectroscopy, UV environmental monitoring, and germicidal cleansing. Detectors and light emitters operating in the solar blind region are of special interest. The solar blind region corresponds to the spectral UV region where strong upper atmospheric absorption of solar radiation occurs, generally at wavelengths between about 200 nm and 290 nm. This creates a natural low background window for detection of man-made UV sources on and proximate to the earth's surface.
Semiconductor materials having a 25° C. band gap of about 4 to 6 eV have been used to sense or generate solar blind UV radiation. Conventional approaches have used semiconductor metal oxides such as AlGaN, MgZnO, or BeZnO, which generally have wurtzite (hexagonal) lattice structures. AlGaN is known to suffer from various problems including cracking due to strain, generally high dislocation density, and lattice mismatch (all such effects are generally interrelated). High dislocation density undesirably reduces internal quantum efficiency. The use of wurtzite MgZnO is limited due to phase segregation that occurs for mid-Mg compositions as a result of solid solubility limits and mixed phase regions. BeZnO is a somewhat more promising material, but has experienced doping difficulties, particularly difficulties in obtaining high mobility and stable p-type doping.